Recent install to MacOS Catalina

You should have a new app on your Mac called Photos. It'll look like this:

Drag your iPhoto Library package onto the Photos icon either in the Dock or in the Applications folder. It will be migrated into a Photos library.

Are you perhaps asking about tethered shooting? How to remotely control your cameras from your Mac?

• For a DSLR camera you would either have to use the software that came with your camera, or use the Image Capture.app to control the camera: Take pictures in Image Capture on Mac - Apple Support
• If you want to take pictures with an iPhone or iPad, and use them instantly on your Mac use the continuity feature. It lest you save new iPhone Photos instantly into a folder in the Finder, or apps like Mail, Messages, etc., see: Use Continuity Camera on your Mac - Apple Support

Use the Photo Booth application.

iPhoto was discontinued 5 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.